Continuous digester



IN V EN TOR.

FRANK B. K. GREEN WMM?% AT '[ORNEYS FIG-1 Sept. 20, 1960 F. B. K.'GREEN commuous DIGESTER 4 Sheets-Sheet 2 Filed July 15, 1955 INVENTOR.

FRANK B.K.GREEN WWW fly;

ATTORNEYS Sept. 20, 1960 F. B. K. GREEN 2,953,202

CONTINUOUS DIGESTER Filed July 15, 1955 4 Shets-Sheet a INVENTOR.

FRANK B.K.GREEN ATTORNEYS FIG-7 Sept. 20, 1960 F. a. K. GREEN 2,953,202

CONTINUOUS DIGESTER Filed July 15; 1955 4 Sheets-Sheet 4 Fl 6 I1 IN V EN TOR.

FRANK B.K. GREEN ATTORNEYS United States Patent CONTINUOUS DIGESTER Frank B. K. Green, Massapequa, N.Y., assignor to Pandia, Inc., New York, N.Y., a corporation of New York Filed July 1955, Ser. No. 522,252

11 Claims. (Cl. 162-237) This invention relates to apparatus for continuously digesting cellulosic materials for use in the manufacture of pulp and paper.

The invention has special relation to the provision of continuous digesting apparatus which will make it possible to effect adequate cooking of the raw cellulosic material in minimum time in order both to obtain maximum strength in the fibers together with maximum yield and also to reduce the size and space requirements for the continuous digesting apparatus. More particularly, since continuous digesting apparatus generally requires an elongated conduit through which the cellulosic materials travel during cooking thereof, the invention contemplates the establishment of cooking conditions. such that the overall time requirements, and therefore the length requirements of the tube, are reduced to a minimum while at the same time the exposure of the fibrous material to the hot chemical atmosphere of cooking is similarly reduced to minimize the loss of useful fibers and the loss of strength in the fiber.

In general, tests in conjunction with the production of pulp from raw cellulosic material such as wood chips have indicated that a chip is capable of absorbing its own weight in digesting liquor. It follows that efiective cooking of the chip as a whole cannot begin until such complete liquor saturation point has been reached, and this time required for such thorough saturating impregnation of the chips is one controlling factor on the overall requirements for cooking time. important from the standpoint of quantity and quality of yield in the cooking process that complete impregnation of the individual chips be accomplished as 'soonas possible after the chips are first heated, since the longer a chip is exposed to heat in the absence of liquor, the greater will be the tendency for acid hydrolysis to take place within the chip as a result of the formation of wood acids such as formic and acetic acids which attack the fiber instead of the lignins and thus cause degradation or deterioration of the fiber. It is therefore essential that such hydrolytic action be minimized by accelerating impregnation of the chips by the digesting liquor in order to check such destructive action.

The desired rapid impregnation of the chips with liquor is facilitated if the chips are treated to eliminate air from the interior thereof, as by exposure to steam, particularly steam at superatmospheric pressure, and itis an object of the present invention to provide apparatus for continuously digesting cellulosic materials wherein the raw material is initially subjected to a preliminary treatment by steam at high pressure to effect rapid elimination of air therefrom wherein the steamed chips are then treated with digesting liquor under controlled conditions in the substantially complete absence of condensate and dilute liquor such that effectively complete impregnation of the chips with liquor is accomplished in minimum time, and wherein the subsequent cooking of the impregnated chips is then carried out at superatmos- In addition it is 2,953,202 Patented Sept. 20, 1960 pheric pressure in a hot vapor-bearing atmosphere substantially free of unabsorbed liquid.

Another object of the invention is to provide continuous digesting apparatus as outlined above such that raw cellulosic material is continuously advanced with accompanying agitation through a plurality of successive treatment zones, the first zone being a heating zone wherein the cellulosic material is subjected to high pressure steam simultaneously with the withdrawal of condensate therefrom a facilitate delivery of the resulting heated material to the next zone substantially free of air bubbles and condensate, the next zone being an impregnation zone comprising in effect a plurality of supplemental zones in each of which liquor is applied to the cellulosic material from above while unabsorbed liquor is drained therefrom from below to assure repeated exposure of all particles of the material to fresh liquor, and the final zone is a cooking zone wherein the liquorimpregnated cellulosic material is exposed to a hot vaporbearing atmosphere substantially free of unabsorbed liquid.

A further object of the invention is to provide an impregnation tube for use in continuous digesting apparatus as outlined above which incorporates perforate false bottom portions throughout the length thereof and defining drainage chambers therebelow within the conduit for effectively continuous draining of condensate and unabsorbed liquor from the cellulosic material advancing therethrough and facilitating separate removal of condensed steam and unabsorbed liquor.

It is also an object of the invention to provide apparatus for the continuous digestion of cellulosic materials as outlined above wherein localized treatment of the raw cellulosic material with steam and with liquor and the removal of condensate and unabsorbed liquor is facilitated by .repeatedlycausing the cellulosic material along the bottom of the treatment zones to form temporary liquid permeable sealing masses retarding flow of unabsorbed liquid lengthwise of the zone and promoting draining of such unabsorbed liquid from each zone directly downwardly to drain outlets.

Additional objects and advantages of the invention will be apparent from the following description, theaccompanying drawings and the appended claims.

In the d n Fig. l is a somewhat diagrammatic view in the nature of a perspective illustrating a complete continuous digesting system in accordance with the invention;

Fig 2 is a side elevational view, partly broken away in vertical section, illustrating the uppermost tube in Fig. 1;

Fig. 3 is an enlarged section on the line 3- 3 of Fig. 2;

Fig. 4 is an enlarged fragmentary section on the line 4-4 of Fig. 3;

Fig. 5 is an enlarged fragment of Fig. 3 showing the mounting of the perforate false bottom within the tube;

Fig. 6 is an enlarged fragment of Fig. 3 illustrating one of the liquor supplying nozzles at the top of the tube;

Fig. 7 is a side elevational view illustrating continuous digesting apparatus in accordance with the invention and embodying a pair of impregnation tubes;

Fig. 8 is an end elevational view looking from right to-left in Fig. 7;

Fig. 9 is a view similar to Fig. 2 and showing another construction of impregnation tube in accordance with the invention;

Fig. l0 is an end view of the tube of Fig. 9; and

Fig. 11 is an enlarged section on the line 11-1 1 of Fig. 9. i

Referring to the drauu'ngs, which illustrate preferred embodiments of the invention, Fig. 1 illustrates a complete system in accordance with the present invention which is generally similar in some aspects to the systems shown in Beveridge et a1. Patent 2,323,194 and the copending application of Frank BHK. Green Serial No.

tube 11 forming the impregnation section of the conduit t and a plurality of cooking tubes 12 and 13 arranged in vertically spaced relation to form the cooking section of the conduit, and a discharge'unit 15 for the digested material,

, jThe feeder 16 in Fig. may be of any typecapable of introducing an efiectively continuous supply of solid material into conduit 11-13 without substantial loss of gas pressure from within the conduit, and it is shown by way of illustration as a pressure feeder of the type shown in the above Beveridge et al. patent. Similarly, the disably accompanied by a defibering action, while maintaining the desired pressure cooking atmosphere within the conduit 1113. The discharge unit 15 is accordingly 'shown by way of illustration as of essentially the construction disclosed in Kehoe et a1. Patent 2,616,802, issued to the assignee of the present application, and which has a drive motor 16 and delivers the cookedand partially defibered pulp to a discharge conduit 17 for conducting such pulp to a refiner or other further treatment station. a

The impregnation tube 11 has special structural characteristics'in accordance with the invention as illustrated charge unit 15 should be of a type capable of effectively continuously discharging the digested material, preferinfFigs. 2-6 which impart special features to the con- 7 struction and operation of the system as a whole. Referring to Fig. 2, the impregnation tube 11 includes a main outer cylinder 20 having an inlet 21 at one end of the upper side thereof and an outlet 22 at the opposite end of'the' lower side of the cylinder, and a hand hole 23 is provided on the side of the cylinder adjacent the outlet 22. Within the cylinder 20 is a perforate false bottom shown as formed by a plurality of arcuately curved perforate plates 25 arranged in end-to-end relaat'22% beyond the vertical center line from the spline tion for convenience of fabrication and removal. These perforate plates 25 are supported along their outer edges by a pair of rods 26, shown as of square section, welded along the sidewall of the cylinder, and the outwardly turned sideedge portions 27 of the plates 25 seat on these rods 26.

The bottom plates 25 extend from the inlet end 0 thecylinder 20 to a position immediatelyadjacent'the outlet 22, and they define in the bottom of the cylinder a crescent-shaped chamber as indicated at 30 in Fig. 3. This chamber 30 is in turn separated into a plurality of individual compartments, identified as 31a to 31f by means of partition plates 32 of generally crescent shape which also cooperate with'reinforcing straps 33 and 34 to form members of generally Z-shape in cross section for supportingthe plates 25 against the pressures thereon incident to use of theunit. As shown in Fig. 4, the strap 33 is welded to the bottom wall of the cylinder 20, the plate 32 is welded to both the straps 33 and 34, and one strap 34 underlies the adjacent ends of each pair of perforate plates 25 and is removably secured thereto by screws 35. As an example of satisfactory dimensions for these parts, in a cylinder 20 having aninner diameter of 35 inches and a wallthickness of V2 inch, the parts 25 and 32-34 may all be formed of quarter-inch plate stock. The outer ends of the two end plates 25 are similarly supported by and secured to channel members 36 otherwise similar to the generally Z-shaped members-32 34. A plurality of inlet ports'40 are provided in spaced and bin 62.

relation'along the upper side of the cylinder 20 for connection to a line for supplying digesting liquor, and these ports 40 are arranged in pairs as shown in Fig. 3. Each port 40 is provided with a spray nozzle 41 for spraying the liquor outwardly and downwardly on the cellulosic material passing therebelow in cylinder 20, each nozzle 41 being supported by a suitable coupling 42 as shown in Fig. 6. In addition, and referring to Fig. 2, the first partition plate 32, is located in a vertical planespaced between the supply inlet 21 and the nearest pair of inlet ports 40, and the first compartment 31a is provided with an individual drain fport 44a, each ofthe remaining compartments 31b-31f having similar drain ports 4412-44 When the impregnation tube 11 is incorporated in a digesting system as shown in Fig. 1, it also includes a Screw conveyor as indicated at 50 in Fig. 1 for causing the cellulosic material which is introduced into the sup- 'ply inlet 21 to be continuously advanced to theoutlet 22 .with accompanying continuous agitation. A drive for the screw conveyor shaft 51' 'is located at one end of the "tube as indicated at 52 in Fig. l and also in F igs. 7-8,

and the other end of the screw, conveyor shaft is supported in a suitable bearing assembly 53. The cooking tubes 12 and 13, which may be cylindrical tubes without special drainage means, also are provided with screw conveyors 50 having similar drive means as indicated in Fig.1. r

' The outer diameter .of the screw conveyor is indifcated at so in Fig. 3 and is somewhat'less than the dis tance betweenthe top of cylinder 20 and the perforate 'plates 25 as measured along a vertical center line. For

example, a screw. conveyor 30 inches in diameter may be used where the inner diameter of. the cylinder 20 is 35 inches, the plates 25 having aninner radius of 16 inches on a center 2% inches above the axis of the cylin- .der, and the screw. conveyor is centered vertically between the plates 25 and the top of the cylinder. Fig. 3

also shows the tube as providedwitha plurality of spline bars 5511-550 which cooperate with the screw conveyor as described hereinafter. 'Three of these spline bars are shown,,the bar 551; being located on the horizontal center line of the cylinder 20 and on' the upturning side of the screw, the spline. bar 55b being located 45 below the spline bar 55a, and the spline bar 550 being located bar-55h. p When the impregnation tube 11.is embodied in a complete system as shown in Fig. 1, the inlet 21 is connected to a T-piece 60 which receives the chips or other raw cellulosic material from thefeeder 10 and its hopper 61 The T-piece 60 also provides a convenient connection for a steam line 63 through which steam at 'superatmosph'eric pressure is admitted to the interior of the tube 111 If, the feeder 10 is generally of the construction described in the above Beveridge et al. patent, it incorporates a feedscre'w or a reciprocating ram which compresses the raw cellulosic material into plug form inthe pipe64 to preven't'substantial loss of pressure from within thetube '11 and T-piece 60. 'With'suchfeeders, a valve 65 may be provided for. preventing the pressure from blowing back. throughth'efeeder in the. event that .the feeder-should stall or otherwise fail to: maintain a properly sealed condition, ,the valve 65 being operated .by a hydraulic cylinder 66-connected to operate automatically in response to a predetermined drop'in the load on: the operating motor for feeder 10. a

-As shown in Fig. 1, each pair o f-inlet ports 40 is connected to a liquor supply line 701 by individual branch a-pump 76 at the liquor tank 77, pump 76 being shown as having its own motor 78.

In accordance with the invention, a special drainage system is provided for the impregnation tube 11. For convenience and flexibility of operation, a main drain header 80 is connected with each. drain port 4411 by individual branch pipes 81a-81f. Each branch pipe 81 includes a control valve 82, and additional control valves 83a-83c are provided in the header: 80-between adjacent pipes 81a-81d to provide for separately controlled drainage from opposite ends of header'80. A drain line 84 for condensate leads from the end of header 80 adjacent the supply inlet 21 to a condensate tank 85, and control valves 86 and 87 operate in unison to provide for intermittent drainage of tank- 85 without loss of the steam pressure within tube 11-.

A second drain line 88 leads from the opposite end of header 80 to the liquor tank 77 i to conduct to tank 77 the relatively dilute liquor which drains from the interior of tube 11 for recirculation to the ports 40 This dilute liquor is reactivated or restored as required to maintain the desired concentration by the addition of fresh liquor from the supply tank 90 by way of a pump and motor 91 and a preheater 92 havinga steam heating connection 93. The specific nature and proportion of the liquor is not a part of the present invention, since the process and apparatus of the invention are applicable to both alkaline and acidic liquors, as well as to straightsteam cooking if desired. The liquor supply system may be provided with suitable automatic controls as indicated by the liquid level control 95 for tank 77 and the rotameter 96.

In the operation of this system as a whole, the raw cellulosic material which is continuously supplied to the T-piece 60 and to the supply inlet 21 of the induction tube 11 is subjected in the T-piece and in the inlet end of tube 11 to the continuous supply of steam at superatmospheric pressure from steam pipe 63. It is therefore rapidly heated, possibly also accompanied by some degree of swelling, with resulting formation of condensate, and the desired elimination of air bubbles from within the chips takes place at the same time. The major portion of this heating action may therefore be controlled to take place before each given section or part1- cle of the cellulosic material has traveled beyond the compartment 31a, and the condensate resulting therefrom will accordingly be drained into compartment 31a for continuous removal by way of pipe 84 to tank 85, the valve 83a being closed to shut this condensate off from the liquor recirculating system. As an illustrative example, the speed and pitch of conveyor screw 50 and the other proportions of tube 11 may be selected to provide an average of approximately three minutes travel for each particle of the raw material in this preheating zone, and during this interval, the material will be continuously agitated by screw 50 to assure repeated exposure of all particles therein to the high pressure steam.

The cellulosic material which has thus been preheated and saturated with moisture, but which is otherwise relatively dry in the sense that it is substantially free of unabsorbed liquid, is then advanced into the series of impregnation zones provided by the other compartments 31b-31f and the inlet ports 40. As the cellulosic material reaches the first pair of ports 40, it will be showered with fresh hot liquor which is substantially immediately absorbed by each particle with which it comes in contact, and the continuous agitation provided by the screw conveyor assures constant change in the surface of the cellulosic material exposed to the liquor. At the same time, some liquor will run through the mass to the drain compartment 31b along with the moisture displaced by the liquor from the swelled cellulosic material, and the resultingpartially dilute liquor will be with- "drawn by way of pipe 81b and drain line 88 to the liquortank 77.

This process is repeated throughout-the advance of the cellulosic material through tube 11. As the material reaches each pair of inlet'ports 40, it is again showered with fresh hot liquor while being alternately raised and tumbled by the screw conveyor so that all parts of the material are assured of exposure to liquor for the desired rapid and thorough impregnation. This result is materially contributed to by the spline bars 55a-5Sc, since they cooperate with the screw conveyor 50 to help move the material forward in the tube at an essentially constant rate by minimizing'the: tendency of the material to revolve in the tube and the resulting slippage. This action also effects localized temporary packing of the cellulosic material along thev perforate plates, 25 in the 'spacebetween these plates and the periphery of the screw conveyor to form a liquid-permeable sealing mass which cooperates with the bafiling eifect of the conveyor screw flights to retard flow of the unabsorbed liquor lengthwise of the tube and thus to promote draining of such unabsorbed liquor from each successive portion of the impregnation zone directly through the adjacent perforate plate 25. This assures that all particles which are not properly impregnated will be successively flooded only with fresh hot liquor rather than with liquor which has already been diluted or otherwise lost a portion of its full strength, thus in turn assuring commencement of a cooking treatment which will be essentially uniform throughout each chip and which therefore can be carried on at maximum speed with equipment of minimum size for the particular results to be obtained.

In the system as shown in Fig. 1, when the cellulosic material reaches the discharge outlet 22 from tube 11, it is thoroughly impregnated by liquor but is essentially free of unabsorbed liquor due to the continuous drainage through the compartments 32. At the same time, the continuous supply of liquor to tube 11 and in the cellulosic material, together with the maintained high temperature and pressure throughout the conduit, establishes a hot vapor-bearing atmosphere throughout the cooking tubes 12 and 13v, and the cellulosic material is dropped throughout the discharge outlet 22 into tube 12 for travel lengthwise thereof and then back through tube 13 to the discharge unit 15 while it is continuously agitated by the screw conveyors in tubes 12 and 13 for repeated exposure of all particles therein to this hot vapor-bearing atmosphere. When this cooking phase of the process has thus been completed, the material is discharged in essentially defibered condition by the discharge unit 15 as described in detail in the above Kehoe et a1. patent.

This system provides great flexibility in the control of all phases of the continuous cooking process. For example, if for some cellulosic material it is desired to increase the time of exposure to steam in the absence of liquor, this may be done by closing the first of the liquor control valves 72 and by opening va-lve 83a and closing valve 83b, thus in effect increasing the length of the presteam-ing zone and adding the condensate from the compartrnent 31b to that from compartment 31a. Conversely, if adequately thorough impregnation for a given raw material is obtained in less than the full length of tube 11, one or more of the last pairs of inlet ports 40 can be shut off to increase the efiective length of the cooking section of the conduit, and the effective lengths of the cooking tubes 12 and 13 can also be varied by regulating the speeds of the screw conveyors therein.

The flexibility of the invention is further illustrated by Figs. 7-8, which show a system in accordance with the invention incorporating a pair of impregnation tubes and 101, each of which may be substantially identical with tube 11 and both of which are accordingly shown as having their component parts designated by the same reference characters as in the case of tube 11 as previously described. The relevant other parts of systemare similarly designated by the same reference characters as in Fig. l. The relative extents of the steaming and 7 impregnation sections of the combined tubes 100 and 101'can be varied as described for tube 11 in accordance the. particular desired conditions to be established and maintained. Thus for particularly large units, it may even be found desirable to use the-upper'tube 100 entirely for steaming the cellulosic material, in which case some or allof the ports 40 may be connected to the steam supply while any of these ports not required for steam can be plugged. The lower tube 101 may then be connected to 9-11 illustrate another construction of impregnation tube which is adapted for use in the system of Figs. 1 and 7 in the practice of-the invention. This tube includes a main cylinder-120 having an inlet 121, an outlet 122 and a hand hole 123 corresponding to the similar parts in the tube of Figs. 2-6, and multiple liquor nozzle means are indicated at 124. This tube is provided with a screw conveyor as indicated at 50, and also the interior of cylinder 120 is provided with a plurality of spline bars 55, four of these bars being shown as located respectively on the horizontal center line of the cylinder, and below center at 45 on either side of the vertical center line of the cylinder. The means for continuously withdrawing condensate and unabsorbed liquor from cylinder 120 comprises a plurality of strainer outlet assemblies identified generally at 125 and shown in more detail in'Fig. 11.

Each of the assemblieslZS includes a short cylindrical tube portion 130 forming a nipple welded to the under side of cylinder 1 20, and cylinder 120 has a cutout 131 coinciding with each nipple 130. The bottom end of each nipple 130 is provided with a flange 132 to which a closure plate 133 is bolted at 134, and the closure plate 133 supports a strainer section 135 shaped and proportioned to fill the cutout 131. This strainer section 135 is mounted on theplate 133 by means of a plurality of studs 136 supported at opposite ends in sockets 137 and 138 welded to the plate 133 and strainer section 135 respectively, the studs 136 being shown as threaded in sockets 138 and secured by set screws in sockets 137.

With this construction, each of the severalnipples 130 inlet end of cylinder 120 is located between the inlet 121 and the first of the nozzle means 124, so that this assembly provides fort-he desired removal of condensate before the cellulosic material within the tube reaches the first zone of liquor treatment. The remaining strainer assemblies 125 correspond to the several additional compartments in Figs. 1 and 2, and the above general discussion with respect to the systems of Figs. l8 applies also to the use of the impregnation tube shown in Figs. 9-11. V

The number and proportions of the strainer assemblies 125 may be variedin accordance with desired operating conditions and the proportions of the impregnation tube as a whole. For example, Fig. 9 shows four of the assemblies 125. equally spaced with respect to each other and with the end assemblies located closely adjacent the inlet 121 and outlet 122 respectively. With the cylinder alsoofierspractical advantages of ease of assembly and..

plate 133 brings with it the associated strainer section'135 for cleaning orother servicing; and this at the same time provides ready access to the interior of the cylinder v a While the forms of apparatus herein described. constitute preferred embodiments of theinvention, it is to be understood that theinvention is not limited to these procise forms of apparatus, and that changes may be made therein'wwithout departing fromthe scope of the invention which is defined in the appended claims. Whatisclaimedis: V r 1. Continuous digesting apparatus for cellulosic materialsfcomprising an elongated generally horizontal tubular conduit having an inlet and an outlet and including an impregnation section and a cooking section adjacent said inlet and outlet respectively, means for continuously feeding raw cellulosic material into said inlet, means for continuouslysupplying steam into said inlet at superatmospheric pressure to efiect rapid heating of said raw cellulosic material with resulting formation of condensate, means including a perforate member in the bottom of said conduit adjacentsaid inlet forming a drain compartment therebelow for receiving said condensate, means located at a plurality of spaced positions lengthwise of said impregnation section for supplying digesting liquor thereto from above, means for effecting continuous advance of said cellulosic material through said impregnation section while continuously agitating said material to cause exposure of all particles therein first to said steam and then to said liquor, all ofsaid liquor supplying means being located downstream from said drain compartment to prevent application of liquor to said material prior to said heating thereof and the drainage therefrom of said condensate into said compartment and thereby to minimize dilution of said liquor and to assure application of said liquor at maximum concentration to said heated and drained material, means including a perforate member forming at least one additional compartment below said impregnation section and spaced from said first compartment, means for separately and continuously with drawing said condensate from said first compartment and the liquor draininginto the'remainder of said compartments while maintaining said superatmospheric steam pressure to assure repeated application of fresh liquor to said cellulosic material from above and to establish a hot vapor-bearing atmosphere in said conduit, and means for eifecting' continuing advance of said cellulosic material throughout said cooking section while agitating said material for repeated exposure of all particles therein to said hot vapor-bearing atmosphere. 7 2. Continuous digesting apparatus for cellulosic materials comprising an elongated generally horizontal tubular conduit having aninlet and an outlet and including an impregnation section and a cooking section adjacent said inlet and outlet respectively, means for continuously feeding raw cellulosic material into said inlet, means for continuously supplying steam into said inlet at'superatmospheric pressure to, efiiect rapid heating of said raw cellulosic material with resulting formation of condensate, means including a perforate member in the bottom of said conduit forming a first draincompartment therebelow for receiving said condensate and at least one additional drain compartment spaced downstream from said first compartment, means located at a plurality of spaced positions lengthwise of said impregnation section for supplying digesting liquor thereto from above, means for efiecting continuous advance .of said cellulosic material through said impregnation section while continuous- 1y agitating'said material to cause repeated exposure of all particles therein first to said steam and then to'said liquor, all of said liquor supplying means being located downstream from at least said first drain compartment to establish a first zone in said conduit for heating of said cellulosic material by steam and drainage of said condensate therefrom in the absence of liquor and thereby to minimize dilution of said liquor and to assure application of said liquor at maximum concentration to said heated and drained material, additional said compartments being spaced lengthwise of said impregnation section to define a plurality of additional successive zones wherein liquor applied to said material from above is drained therefrom from below before advance of said material to the next zone, means for selectively controlling said liquor supplying means to provide for treatment of said material with steam in the absence of liquor in selected said zones adjacent said first zone, separate drain outlets from each said compartment, selective control means for said drain outlets providing for continuously withdrawing condensate from said first compartment and each adjacent zone wherein no liquor is supplied and for continuously withdrawing liquor from said compartments in the remainder of said zones While maintaining said superatmospheric steam pressure to establish a hot vapor-bearing atmosphere throughout the remainder of said conduit, and

means for effecting continued advance of said cellulosic material through said cooking section while agitating said material for repeated exposure of all particles therein to said hot vapor-bearing atmosphere.

3. In continuous digesting apparatus for cellulosic materials, the combination of an elongated impregnation tube, means defining an inlet at one end of the upper side i of said tube and an outlet at the opposite end of the lower side of said tube, means for continuously supplying raw cellulosic materials and steam to said inlet to effect rapid heating of said material with resulting formation of condensate, means for advancing said material from said inlet to said outlet while agitating said material, perforate means extending within the bottom of said tube from said inlet end thereof to said outlet in upwardly spaced relation with the wall of said tube to form a perforate false bottom defining a chamber therebelow for receiving liquid draining therethrough, a plurality of inlet ports spaced along the upper side of said tube from a position adjacent said inlet to a position adjacent said outlet for connection to liquor supplying means, a plurality of generally radially arranged partitions separating said chamber into a plurality of compartments, the first said partition being located adjacent said inlet to define a first zone in said tube extending from said inlet to sm'd first partition and a first compartment below said first zone for draining said condensate from said material prior to advance of said material therebeyond, the nearest said inlet port to said inlet being located downstream from said first partition to prevent application of liquor to said material prior to said heating thereof in said first zone and the drainage of said condensate therefrom into said first cornpartment and thereby to minimize dilution of said liquor and to assure application of said liquor at maximum concentration to said heated and drained material, additional said partitions being spaced lengthwise of said tube for cooperation with said inlet ports to define a plurality of further successive zones wherein liquor applied to material from above is drained therefrom from below before advance of said material to the next said zone, the last said partition being located between the last said inlet port and said outlet to minimize transmission of unabsorbed liquor to said outlet, and separate drain ports from each said compartment.

4. Continuous digesting apparatus for cellulosic materials comprising an elongated generally horizontal tubular conduit having an inlet and an outlet at opposite ends in said first zone with resulting formation of condensate for draining into said compartment, means for continuous ly withdrawing said condensate from said first compartment, means located at a plurality of spaced positions lengthwise of said intermediate zone for continuously supplying digesting liquor thereto from above, all of said liquor supplying means being located downstream from said first compartment to prevent application of liquor to said material prior to said heating thereof and the drainage of said condensate therefrom into said first compartment and thereby to minimize dilution of said liquor and to assure application of said liquor in said intermediate zone at maximum concentration to said heated and drained material, means for effecting continuous advance of said cellulosic material through said first and intermediate zones while continuously agitating said material to cause repeated exposure of all particles therein first to said steam and then to said liquor, means including a perforate member in the bottom of said intermediate zone forming a second compartment therebelow for receiving unabsorbed liquor draining therethrough, means for continuously removing the liquor draining into said second compartment while maintaining said superatmospheric steam pressure to assure repeated application of fresh liquor to said cellulosic material from above while establishing a hot vapor-bearing atmosphere throughout said conduit, and means for continuing the advance of said cellulosic material throughout said third zone while agitating said material for repeated exposure of all particles therein to said hot vapor-bearing atmosphere.

5. Continuous digesting apparatus as defined in claim 4 comprising means for effecting localized temporary packing of said cellulosic material along the bottom wall of said first and intermediate zones in conjunction with the advance thereof to form a liquid-permeable sealing mass of said material along said wall retarding flow of unab sorbed liquor lengthwise of said zones and promoting draining of such unabsorbed liquor directly to said second compartment. 7

6. Continuous digesting apparatus as defined in claim 4 wherein said means for effecting advance of said cellulosic material through said first and intermediate zones-comprises screw conveyor means extending lengthwise of said first and intermediate zones, and a plurality of splines extending generally axially of said two zones and projecting radially inwardly from the inner wall of the lower portion of said conduit in circumferentially spaced relation for cooperation with said screw conveyor means to effect localized temporary packing of said cellulosic material along the bottom of said intermediate zone into a liquid-permeable sealing mass of said material retarding fiow of unabsorbed liquor lengthwise of said zones and promoting draining of such unabsorbed liquor directly to said second compartment.

7. An impregnation tube for use in continuous digesting apparatus for cellulosic materials comprising an elongated main cylinder, means defining an inlet for cellulosic material and steam at one end of the upper side of said cylinder and an outlet at the opposite end of the lower side of said cylinder, means including a perforate member in the bottom of said cylinder forming a plurality of compartments therebelow for receiving liquid draining therethrough, a plurality of inlet ports spaced along the upper side of said cylinder from a position adjacent said inlet to a position adjacent said outlet for connection to liquor supplying means, the first said compartment being located between said inlet and the nearest said inlet port to define a first zone in said tube providing for drainage of liquid from material within said first zone prior to passage of material therebeyond and thereby preventing application of liquor to said material prior to said drainage thereof in order to minimize dilution of said liquor and to assure application of said liquor at maximum concentration to said drained material, the other said compartments being spaced lengthwise of said cylinder to 1.1 r definewiththe remainder of said inlet ports a plurality of further successive zones wherein liquorapplied to ma terial within said cylinder from above is drained therefrom from below before advance of said material to the next said zone, and a separate drain outlet from each said compartment. 4

8. An impregnation tube for use in continuous digesting apparatus for cellulosic materials comprising an elongated main cylinder, means defining an inlet for cellulosicmaterial and steam at one end of the upper side of said cylinder and'an outlet at the opposite end of the lower side of said cylinder, perforate means extending within the bottom of said cylinder from said'inlet end thereof to said outlet in upwardly spaced relation with the wall-of said compression, the first said partition being located between said inlet and the nearest said inlet port to define a first zone in said tube providing for drainage of liquid from material within said first zone prior to passage of material therebeyond and thereby preventing application of liquor to said material prior to said drainage thereof in order to minimize dilution of said liquor and to assure application of said liquor at maximum concentration to said drained material, additional said partitions being spaced I lengthwise of said cylinder to define with the remainder of said inlet portsa plurality of further successive zones wherein liquor applied to material'from above is drained therefrom from below before advance of said material to the next said zone, andseparate drain outlets from each said compartment.

a 9. An impregnation tube for use in continuous digesting apparatus for cellulosic material comprising an elongated main cylinder, means defining an inlet at one end of the upper side of said cylinder for receiving said material and an outlet at the opposite end of the lower side of said cylinder for discharging said material, perforate means extending within the bottom of said cylinder from said inlet end thereof to said outlet in upwardly spaced relation with the wall of said cylinder to form a perforate false bottom defining a chamber therebelow for receiving liquid draining therethrough, a plurality of inlet ports spaced along the upper side of said cylinder from a position adjacent said inlet to a position adjacent said outlet for connection to liquor supplying means, a

plurality of generally radially arranged partitions separating said chamber into a plurality of compartments and supporting said perforate means against compression, the

first said partition being located between said inlet and the nearest said inlet port to define a first zone in said tube, additional said partitions being spaced lengthwise of said cylinder to define a plurality of further successive zones wherein liquor applied to material from above is drained therefrom from below before advance ofsaid material to the next said zone, a screw conveyor extending lengthwise of said tube for causing said material to advance from said inlet to said outlet, a plurality of splines extending generally axially of said tube and projecting radially inwardly from said perforate means in circumferentially spaced relation 'for' cooperation with said screw conveyor =to etfectlocalized packing of said cellulosic material along said perforate means into a liquid-permeable sealing mass of said material retarding flow of unabsorbed liquor lengthwise of said tube and promoting draining of such unabsorbed liquor from each said zone directly to the associated said compartment, and separate drain outlets from each said compartment.

10. An impregnation tube for use in continuous digesting apparatus for cellulosic materials comprising an elongated main cylinder, means defining an inlet at one end of the upper's'ide of said cylinder and an outlet at the opposite endof the lower side of said cylinder, said cylinder having a plurality of drain openings located in spaced relation along the bot-tom thereof, a nipple secured to the under side of said cylinder at each said drain opening, a closure removably secured to the lower end of each said nipple and cooperating therewith to form a drain compartment, a perforate member carried by each said closure and supported thereby within the associated said drain opening for transmitting liquid therethrough while retaining said material within the interior of said cylinder, and means forming a separate drain outlet from each said compartment. 4

11. A strainer assembly for incorporation with an impregnation tube for use in continuous digesting apparatus for cellulosic materials and including an elongated main cylinder having an inlet at one end of the upper side of said cylinder and an outlet at the opposite end of the lower side of said cylinder and also having at least one drain opening located in the bottom thereof, comprising a nipple adapted to be secured to the under side of said cylinder at each said drain opening, a closure plate removably secured to the lower end of said nipple for cooperation therewith to form a drain compartment, a perforate member proportioned to be received within 'said drain opening, means supporting'said perforate member on and in upwardly spaced relation from said closure plate to locate said perforate member within said drain opening for transmitting liquid there through whileretaining said cellulosic material within the interior of said cylinder, and means forming a drain outlet from said compartment.

References Cited in the file of this patent UNITED STATES PATENTS France .Apr. 25,

OTHER REFERENCES Paper Trade Journal, Nov. 6, 1947, page 77.

' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2353 202 September 20 1960 Frank B. Ko Green It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 line 1O for a" read to column 6 line 35, for "32" read 31 -=e Signed and sealed this 11th day of April 1961s SEAL) Attest:

ERNEST SW'DER ARTHUR w. CROCKER Attesting Officer A i Commissioner of Patents 

